Expansion tanks are commonly used in heating, cooling and air condition systems to avoid unacceptable increase of system pressures during heat-up, generally by absorbing expanding fluid and limiting pressure within the system. Expansion tank designs include open tanks, closed compression tanks and diaphragm tanks.
In a diaphragm expansion tank, a diaphragm or bladder is used to separate air from water within the tank. In particular, one side of the tank is connected to piping of a heating system (or cooling/air condition system) and therefore contains the water, while the other side contains air under pressure. A Schrader valve is typically provided at the air side of the tank for checking pressure and adding air, which allows the pressure of the tank to be adjusted as needed.
An air/gas charge pressure on one side keeps the diaphragm at a distance away from the inside wall of the tank in the gas side. When the tank is installed onto a water system, the water system pressure pushes back against the diaphragm, compressing the gas. When the system is cold and the water in the tank is at the minimum level, the tank pressure is at an initial/pre-charge pressure. As the temperature in the system increases, the water expands to compress the gas chamber via the diaphragm, causing an increase in the gas and water system pressure.
However, the diaphragm has a limited life. If eventually the diaphragm “bottoms out” on the tank wall, the tank becomes ineffective in the function it has been design to provide. Various failure modes for expansion tanks include incorrect precharge pressure (e.g. a low air precharge), excessive system pressure, diaphragm failure resulting in leak of air charge, and installation of an incorrectly sized tank (e.g. undersized tank which causes the diaphragm to overwork), all of which can lead to quick cycling and ultimately failure. In such failure modes, the diaphragm can develop a pinhole, an abrasion, a cut or the like that allows water to enter the gas side of the tank. Over time, the gas will be absorbed into the water system and the gas charge will decrease to zero. At this point, the tank is considered ineffective. This can eventually cause failure of other equipment in the system or failure of the tank itself, resulting in water leakage into space surrounding the tank.
In order to determine whether there are problems in the expansion tank operation or if the expansion tank has failed, a homeowner must often require the services of a plumber to remove the tank from the system and perform tests. This is time consuming and expensive. It would, thus, be beneficial to provide a mechanism that makes it easier for a homeowner or a plumber to determine whether an expansion tank has operational problems or has failed, thus enabling more pro-active maintenance of the equipment. Such a mechanism can also beneficially alert a user to early problems in the tank, which can potentially be addressed to prevent tank failure.